Method of extruding consumable anodes with anodized core-cladding interface

ABSTRACT

An extrusion process for forming consumable anodes and the product produced therein. The process comprises the co-extrusion of a wire core having a non-ferrous light metal surface with an overcoating of a dissimilar light metal. A synthetically produced non-ferrous metal oxide layer is interposed between the dissimilar light metal surfaces to reduce the incidence of core wire breakage during extrusion operations. It is believed that alloying of the light metal core surface with the dissimilar extruded overcoating is inhibited by the oxide layer, thereby substantially eliminating adherence of a low melting, non-ferrous alloy to the extrusion die. Breakage of the core wire during extrusion is thereby minimized.

United States Patent [1 1 Pashak Oct. 15, 1974 [75] Inventor: John F. Pashak, Linwood, Mich.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

22 Filed: Oct. 24, 1972 21 Appl. No.: 299,881

Related US. Application Data [62] Division of Ser. No. 92,305, Nov. 23, 1970, Pat. No.

Primary Examiner-Charles W. Lunham Assistant Examiner-Robert M. Rogers Attorney, Agent, or FirmWilliam M. Yates; Robert W. Selby; Lloyd S. Jowanovitz [5 7 ABSTRACT An extrusion process for forming consumable anodes and the product produced therein. The process comprises the co-extrusion of a wire core having a nonferrous light metal surface with an overcoating of a dissimilar light metal. A synthetically produced nonferrous metal oxide layer is interposed between the dissimilar light metal surfaces to reduce the incidence of core wire breakage during extrusion operations. It is believed that alloying of the light metal core surface with the dissimilar extruded overcoating is inhibited by the oxide layer, thereby substantially eliminating adherence of a low melting, non-ferrous alloy to the extrusion die. Breakage of the core wire during extrusion is thereby minimized.

10 Claims, 3 Drawing Figures cepted.

METHOD or EXTRUDING CONSUMABLE ANODES wrrrr ANODIZED CORE-CLADDING INTERFACE CROSS-REFERENCE TO RELATED APPLICATION This is a division, of application Ser. No. 92,305 filed Nov. 23, 1970, now U.S. Pat. No. 3,723,282.

BACKGROUND OF THE INVENTION This invention relates to extrusion and more specifically to the extrusion of consumable anodes and the products produced thereby.

Anodes have been produced by various methods in-' cluding casting, extruding, and fabrication of the individual components. The completed anode product is commonly used to minimize corrosion by cathodic protection of water heaters, underground metallic pipes, or ships hulls. In operation, the consumable anode is usually positioned so as to be in electrical contact with the metal to be protected. Protection of the'metal is effected by preferential corrosion attack of the anode.

Previously, metals such as aluminum, magnesium, zinc, alloys thereof and combinations of these metals have'been advantageously used in the preparation of consumable anodes. Additionally, light metal anodes having ferrous or aluminized ferrous cores are known. A method and apparatus for producing an extruded magnesium anode with an aluminum coated steel core wire is described in US. Pat. No. 2,841,546. FIG. 1 of the drawing depicts a longitudinal section of an extrusion apparatus and die of US. Pat. No. 2,841,546. FIG.

ram 15.-The magnesium is passed from within a cylinder 16 through four portholes 17 and into a mixing chamber 18 before passing through the die .orifice 12 to form the extruded anode 14. The useful life of an aluminized steel cored magnesium anode is often superior to the simple ferrous cored anode.

One of the major difficulties encountered in producing bimetallic aluminum-magnesium overcoated black iron or steel wire anodes is breakage of the wire during extrusion. The wire breakage has been so extreme and costly that processing using the alum'inized'ferrous wire with a non-ferrous cladding, or a bimetallic aluminummagnesium combination not been generally ac- It is an object of this invention to provide a method for co-extrusion of dissimilar non-ferrous metals without excessive breakage of the core wire during extru- SlOI'l. i

Another object is to provide a method for extruding ferrous wire having a light metal coated surfaceand a dissimilar-non-ferrous metal overcladding without excessive breakage during extrusion;

Other objects andadvantages will become apparent during the course of the following description.

SUMMARY O THE INVENTION The aforementioned difficulties have been surmounted and objects realized by the instant invention which comprises passing a continuous metal core, having a light metal surface, through adie of larger crosssection than the metal core and simultaneously extruding a light metal with the metal core, whereby an overcoating of light metal is applied to the continuous metal core; the light metal surface of the metal core having been anodized to produce a synthetic oxide layer prior to its passing through the extrusion die. The light metals used in this method can be dissimilar. Employable dissimilar light metals are alloys of either aluminum "or magnesium containing at least 50 percent of the base metal.

Artificially formingan oxide coating of a light metal on the core surface or undercoating in which the inner core is positioned, was found to satisfactorily inhibit alloying of aluminum and magnesium during subsequent extrusion. The synthetically oxidized protective film, therefore, permits contact of the dissimilar non-ferrous metal surfaces at extrusion temperatures and pressures without the formation of a sufficient quantity of an aluminum-magnesium alloy, which melts at a lower temperature than either of the alloy constituents, to result in enough build-up in the extrusion die orifice to cause core wire breakage.

An extrusion is produced which comprises a meta core having a light metal surface and an overcoating of a light metal. At least one of the interfacing surfaces between the light metal surface of the core'and the inner surface of the cladding has a coating of a synthetically produced oxide of the underlying light metal; The light metal in the consumable'electrode is usually an aluminum alloy or magnesium alloy.

It is postulated that at least part of the success of this product resultsfrom' the oxide coating being discontin- PREFERRED EMBODIMENT In the process of the current invention it is preferred the core materials be a ferrous material coated with an aluminum alloy. The aluminum coating on the ferrous core may be achieved by a means such as spraying, dipping, or casting the aluminum around the wire. Examples of suitable materialsfor ferrous base wires are steel and black iron. Commercially purchased. aluminized black iron wire can also be used successfully this process. 1

The specific method of forming oxide on' the nonferrous' inner layer adhering to the exterior of the ferrous core wire or to the exterior surface of the nonferrousbase inner core wire is'not critical. Examples of suitable oxide application methods are anodizing, and heating in an oxygen containing atmosphere. It'is of importance though that the oxide layer befat least 0.0002

inch thick to'adequately protectagainstalloying of the rnagnesiumandaluminurngwhile being extruded at ings of greater thickness than 0.001' inch are employ-' able in this invention, however, the additional depth is believed to be superfluous. A sufficient coating of oxide must be present on the light metal surface to hinder the accumulation of enough intermetallic aluminum-magnesium composition in the die orifice to cause wire breakage during extrusion.

To achieve the greatest benefit from the instant invention it is preferred that a magnesium base alloy overcladding surround the generally axially aligned oxidized aluminized ferrous wire. This combination will provide improved strength of the completed anode and retain the beneficial corrosion protection properties of magnesium.

Coating the generally axially aligned iron base core with a magnesium alloy, anodizing the magnesium layer, and co-extruding the magnesium coated iron base wire with an outer layer of an aluminum alloy will also produce acceptable results. A magnesium undercoating can be achieved by casting a magnesium alloy around a zinc galvanized iron base wire.

Example l An aluminum base alloy, registered with The Aluminum Association as 5356, having a nominal composition of 5.0 percent magnesium, 0.12 percent manganese, 0.12 percent chromium, and 0.12 percent titanium was employed in accord with this invention. A 5356 alloy wire 3/32 inch diameter by feet long was anodized in sulfuric acid to produce an oxide coating 0.00l inch thick on the surface of said wire. After anodizing, the wire was fed into an orifice in a three port anode extrusion die in a 500 ton laboratory extrusion press to form an anode core. A magnesium alloy containing at least 99.5 percent magnesium was extruded around the anodized 5 356 alloy aluminum wire to produce a 1 inch diameter anode.

The extrusion die and extrusion billet container were preheated to a temperature of 900F. The magnesium billets were preheated to a temperature of 950F. prior to extruding. Continuous extrusions having a magnesium overcoating and 5356 alloy aluminum core wire were produced without wire breakage. The die orifice was examined and the previously common aluminum-magnesium intermetallic compound was not apparent. Examples 2-6 Aluminum 5356 alloy wire was positioned within an orifice in a three port extrusion die in a 500 ton extrusion press and simultaneously extruded with a magnesium alloy having an ASTM designation of AZ31B and a nominal composition of 3 percent aluminum, 1 percent zinc, and 0.4 percent manganese. Prior to extrusion the 53 56 wire was anodized in sulfuric acid by standard'procedures to cause an oxide surface layer to form. Depths of the oxide layers utilized herein are shown in the table. AZ3lB ingot was preheated to a temperature of 850F. before being passed through a die orifice heated to 800F. at a speed of 5 feet per minute. g

The extruded product was a 1 inch diameter composite having an anodized 5356 alloy core and a cladding of A23 l B magnesium alloy. An anode product was extruded employing aluminum core wire, which had been anodized to form aluminum oxide on the surface to the hereinafter listed depths, without wire breakage.

Extrudahility of Anodized 5356 Aluminum Core and Magnesium A23 lB Cladding Wire Breakage H 50 Anodized Core Quring Extrusion Application Time Oxide Thickness What is claimed is:

l. A method to minimize core breakage during extrusion which comprises passing a continuous metal core having a light metal surface through a die of larger cross section than the metal core and simultaneously extruding a light metal with the metal core whereby an overcoating of light metal is applied to the continuous metal core, the light metal surface of the metal core having been anodized to produce a synthetic oxide layer thereon prior to its passing through the extrusion die, the light metals being aluminum alloys and magnesium alloys. i

2. The method of claim 1 wherein the metal core is a ferrous base alloy.

3.The method of claim 2 wherein the ferrous base alloy is coated with an aluminum alloy and the overcoating is a magnesium alloy.

4. The method of claim 1 wherein said core is an aluminum alloy and said overcoating is a magnesium alloy.

5. The method of claim 1 wherein said synthetic oxide layer is at least 0.0002 inch in thickness.

6. A method to extrude a composite consumable anode and minimize core wire breakage during extrusion comprising passing a continuous metal core having a light metal surface through a die of larger cross section than the metal core and simultaneously extruding a light metal with the core whereby an overcoating of light metal is applied to the continuous metal core, the light metal surface of the metal core having thereon a synthetic oxide layer at least 0.0002 inch in thickness and sufficient to inhibit alloying of the oxide coated light metal with the adjacent light metal during extrusion, the light metals being aluminum alloys and magnesium alloys, thereby minimizing sufficient aluminummagnesium intermetallic compound build-up in the die orifice to cause wire breakage during extrusion.

7. The method of claim 1 wherein the oxide layer is from about 0.0004 to about 0.001 inch thick.

8. The method of claim 3 wherein the oxide layer is from about 0.0004 to about 0.001 inch thick.

9. The method of claim 1 wherein the oxide layer is at least about 0.0002 inch in thickness and sufficient to minimize wire breakage during extrusion.

10. The method of claim 1 wherein the oxide layer is at least about 0.0002 inch in thickness and an effective anode with an intermediate fractured light metal oxide layer interposed between the core and the overcoating is produced. I I 

1. A METHOD TO MINIMIZE CORE BREAKAGE DURING EXTRUSION WHICH COMPRISES PASSING A CONTINUOUS METAL CORE HAVING A LIGHT METAL SURFACE THROUGH A DIE OF LARGER CROSS SECTION THAN THE METAL CORE AND SIMULTANEOUSLY EXTRUDING A LIGHT METAL WITH THE METAL CORE WHEREBY AN OVERCOATING OF LIGHT METAL IS APPLIED TO THE CONTINUOUS METAL CORE, THE LIGHT METAL SURFACE OF THE METAL CORE HAVING BEEN ANODIZED TO PRODUCE A SYNTHETIC
 2. The method of claim 1 wherein the metal core is a ferrous base alloy.
 3. The method of claim 2 wherein the ferrous base alloy is coated with an aluminum alloy and the overcoating is a magnesium alloy.
 4. The method of claim 1 wherein said core is an aluminum alloy and said overcoating is a magnesium alloy.
 5. The method of claim 1 wherein said synthetic oxide layer is at least 0.0002 inch in thickness.
 6. A method to extrude a composite consumable anode and minimize core wire breakage during extrusion comprising passing a continuous metal core having a light metal surface through a die of larger cross section than the metal core and simultaneously extruding a light metal with the core whereby an overcoating of light metal is applied to the continuous metal core, the light metal surface of the metal core having thereon a synthetic oxide layer at least 0.0002 inch in thickness and sufficient to inhibit alloying of the oxide coated light metal with the adjacent light metal during extrusion, the light metals being aluminum alloys and magnesium alloys, thereby minimizing sufficient aluminum-magnesium intermetallic compound build-up in the die orifice to cause wire breakage during extrusion.
 7. The method of claim 1 wherein the oxide layer is from about 0.0004 to about 0.001 inch thick.
 8. The method of claim 3 wherein the oxide layer is from about 0.0004 to about 0.001 inch thick.
 9. The method of claim 1 wherein the oxide layer is at least about 0.0002 inch in thickness and sufficient to minimize wire breakage during extrusion.
 10. The method of claim 1 wherein the oxide layer is at least about 0.0002 inch in thickness and an effective anode with an intermediate fractured light metal oxide layer interposed between the core and the overcoating is produced. 